This invention relates generally to a hydraulic drive for vehicles, and more particularly to such a drive which is effected by rotary vanes pumps used as a primary drive pump and as driven pumps associated with each of the vehicle wheels.
Rotary vanes pumps of various designs have in the past been designed as fluid motors for powering vehicles. Slidable radially extending vanes are normally provided on the rotor, and the vane tips are constantly urged by springs into contact engagement with a cam surface of the stator. Such fluid drives are typically shown in U.S. Pat. Nos. 3,702,642; 3,680,652; 3,280,934; 3,185,241; 2,791,284 and 2,655,785.
A typical drawback exists for each of these prior art rotary vanes pumps or motors, e.g., a specific cam surface must be machined for the stator which is costly and often times imperfect, and wearing of both the blade tips and the cam surface occurs as the vanes constantly bear against the surface under the action of springs provided in the vane slots. Undue wear of the parts result and the springs quickly deteriorate as they are constantly expanding and contracting during rotor movement. Moreover, the relative complexities of the prior art designs render them undesirable for use as both a primary drive pump for the hydraulic system and as driven pumps or motors associated with each of the wheels.